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  • 剑指offer 61.树 序列化二叉树

    题目描述

    请实现两个函数,分别用来序列化和反序列化二叉树
     
    二叉树的序列化是指:把一棵二叉树按照某种遍历方式的结果以某种格式保存为字符串,从而使得内存中建立起来的二叉树可以持久保存。序列化可以基于先序、中序、后序、层序的二叉树遍历方式来进行修改,序列化的结果是一个字符串,序列化时通过 某种符号表示空节点(#),以 ! 表示一个结点值的结束(value!)。

    二叉树的反序列化是指:根据某种遍历顺序得到的序列化字符串结果str,重构二叉树。
     

    代码如下

    //采用层序遍历,不需要将转化为完全二叉树的简单方法
    public class Solution {
        String Serialize(TreeNode root) {
            StringBuilder sb = new StringBuilder();
            Queue<TreeNode> queue = new LinkedList<TreeNode>();
            if(root != null)
                queue.add(root);
            while(!queue.isEmpty()){
                TreeNode node = queue.poll();
                if(node != null){
                    queue.offer(node.left);
                    queue.offer(node.right);
                    sb.append(node.val + ",");
                }else{
                    sb.append("#" + ",");
                }
            }
            if(sb.length() != 0)
                sb.deleteCharAt(sb.length()-1);
            return sb.toString();
      }
        TreeNode Deserialize(String str) {
           TreeNode head = null;
            if(str == null || str.length() == 0)
                return head;
            String[] nodes = str.split(",");
            TreeNode[] treeNodes = new TreeNode[nodes.length];
            for(int i=0; i<nodes.length; i++){
                if(!nodes[i].equals("#"))
                    treeNodes[i] = new TreeNode(Integer.valueOf(nodes[i]));
            }
            for(int i=0, j=1; j<treeNodes.length; i++){
                if(treeNodes[i] != null){
                    treeNodes[i].left = treeNodes[j++];
                    treeNodes[i].right = treeNodes[j++];
                }
            }
            return treeNodes[0];
      }
    }
     
    //前序遍历
    public class Solution {
        String Serialize(TreeNode root) {
            StringBuilder sb = new StringBuilder();
            getSerializeString(root, sb);
            if(sb.length() != 0)
                sb.deleteCharAt(sb.length()-1);
            return sb.toString();
          }
        getSerializeString(TreeNode root, StringBuilder sb){
            if(root == null)
                sb.append("#,");
            else{
                sb.append(root.val + ",");
                getSerializeString(root.left, sb);
                getSerializeString(root.right, sb);
            }
        }
        TreeNode Deserialize(String str) {
           if(str == null || str.length() == 0 || str.length() ==1)
                return null;
            String[] nodes = str.split(",");
            TreeNode[] treeNodes = new TreeNode[nodes.length];
            for(int i=0; i<nodes.length; i++){
                if(!nodes[i].equals("#"))
                    treeNodes[i] = new TreeNode(Integer.valueOf(nodes[i]));
            }
            Stack<TreeNode> stack = new Stack<>();
            stack.push(treeNodes[0]);
            int i = 1;
            while(treeNodes[i] != null){
                stack.peek().left = treeNodes[i];
                stack.push(treeNodes[i++]);
            }
            while(!stack.isEmpty()){
                stack.pop().right = treeNodes[++i];
                if(treeNodes[i] != null){
                    stack.push(treeNodes[i++]);
                    while(treeNodes[i] != null){
                        stack.peek().left = treeNodes[i];
                        stack.push(treeNodes[i++]);
                    }
                }
            }
            return treeNodes[0];
          }
    }
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  • 原文地址:https://www.cnblogs.com/Transkai/p/11422305.html
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